This invention generally relates to the recycling and use of roofing waste, including shingles, tar paper and portions thereof with gravel to make a pavement composition. More specifically, the invention relates to the use of recycled asphalt shingles, or a blend of recycled asphalt shingles and recycled asphalt product in a novel method of making a pavement composition that does not require the addition of asphalt concrete oil (AC oil or virgin AC oil) apart from recycled products containing AC oil to make hot mix asphalt, or in the alternative, minimizes the addition of AC oil necessary to make hot mix asphalt.
Methods and apparati for manufacturing asphalt paving compositions for roadways and the like are well known. Virgin aggregate is utilized, which is largely comprised of crushed rock, small rock, and sand generally one inch in diameter and down to a sieve size of 200. Three quarter inch in diameter is often preferable. Typically, virgin aggregate is heated between 220° to 350° F. and dried in a rotating drum. Asphalt or asphalt-concrete oil is utilized with various penetration numbers ranging from 85 to 150, and which is also heated to a range of 280° to 350° F. The heated aggregate is then mixed with liquid asphalt in a proportion typically of five to six percent asphalt by weight. The paving composition is then hauled with trucks to the job site and dumped into a paving vehicle. The paver lays the hot mix out level to a desired thickness on top of a graded gravel surface of a suitable evaluation and smoothness. Thereafter the new pavement is compacted with a roller to the desired density.
Roofing materials, including shingles, tar paper and portions thereof, also utilize asphalt. The asphalt is commonly an asphalt-concrete oil (“AC oil”) which is heavy and tar-like. Shingles are composed of a mat that may either be fiberglass or of a paper felt-like material. Initially the paper felt-like material is soaked with a light saturine oil, whereas fiberglass is not. Thereafter, a layer of asphalt-concrete oil is applied thereto. Next a layer of lime dust is placed or dusted thereon. Another layer of AC oil is applied afterwhich a rock layer is applied. Thereafter, the entire composition is run through rollers.
Considerable roof waste (RARW—Recycled Asphalt Roofing Waste; or RAS recycled asphalt shingles) is associated with the manufacture of new shingles, which may approximate one hundred million squares annually. A square is one hundred square feet of shingles. Each shingle has three tabs cut out. Each cutout tab measures one-quarter inch by five inches. The three discarded tabs (RAS) represent approximately two and a half percent of each new shingle which is discarded. When old shingles and tar paper are removed from old construction, the one to three layers of shingles are all considered waste and are to be disposed of. Thus old shingle materials, also RARW, represent an even larger amount of waste associated with shingle materials. Shingles typically have 17-30% w of asphalt oil of the total shingles weight. An average asphalt or weight to total shingle weight is 20%.
Methods and apparati have been disclosed by which old shingles and shingle material have been attempted to be recycled, such as those shown in U.S. Pat. Nos. 4,222,851; 4,706,893; 4,726,846; 5,201,472; 5,217,530; and 5,236,497. Illustratively, the '893 patent shows a method and apparatus wherein recycled shingles may be used in an asphalt plant mixed with heated and dried aggregate and liquid asphalt to form an asphalt paving composition. However, these prior methods of creating pavements and apparati have not been commercially successful for various reasons and especially due to their inability to handle shingles without clogging or plugging up apparati.
Prior art pavements utilizing RARW or Recycled Asphalt Roofing Waste are plagued with the two basic problems of air voids and stabilization. Air voids generally may be thought of as air pockets in the pavement. The air pockets must not be too tight or there will not be enough room to allow the pavement to move or slightly expand during freezing. If the air voids or air pockets are too loose, the pavement will be highly susceptible to water. Air voids in the range of two to eight percent are ideal and the prior art mixtures have had problems in attaining this acceptable range.
With respect to stabilization or firmness of the pavement material, the pavement material must not be too firm or it will not be workable in application as a pavement. Conversely, the material must have some degree of firmness or it will not set up for traffic use and will result in rutting. A stabilimeter value of 800 to 3000 is acceptable and the prior art pavement mixtures and materials have had difficulty in consistently reaching this range.
The aggregate utilized is of a range of size from one inch to two hundred sieve size. The aggregate's porosity may also vary greatly. Furthermore, the aggregate may carry water or a significant amount of moisture into the mixture which causes problems. The condition of the RARW or shingle materials greatly affects the mixture. Older shingle materials commonly are oxidized and may have a significantly reduced AC oil content. Also, shingle materials may carry moisture, which also poses the problem described above. Some of these problems may be solved by conceivably superheating the mixture. Emulsifiers may be used for RARW having 10% or greater water weight of the total RARW weight.
The inventor obtained U.S. Pat. Nos. 6,186,700 and 6,588,973. These patents disclosed and claimed methods of manufacturing and applying a pavement and patch material for roadways, driveways, walkways, patch for potholes and like surfaces, including the steps of reducing recycled asphalt roof waste to granules, adding aggregate and other solid recyclable materials to the granules, adding rejuvenating oil, adding emulsifier, adding asphalt concrete oil, adding anti-strip additives, adding liquid silicone, mixing the composition, heating the composition, applying the composition to the roadway or the like and compacting a new paving material. All patents referred to herein this application are incorporated herein as though repeated herein.
In the hot mix asphalt (HMA) industry, there are two types of asphalt plants that make the bituminous product. There is a mix drum apparatus and a batch plant, both use a particular conventional sequence of events to produce the product HMA. First, the gravel is heated. Then processed shingles and recycled asphalt products (RAP) are added to the heated gravel, allowing time for the hot gravel to activate the asphalt concrete oil (AC oil) in the processed shingle/RAP mixture. Next, additional AC oil, not contained in the processed shingle/RAP mixture or processed shingles, and other oil products (such as rejuvenating oils) are added to make the HMA.
The conventional method does not extract the most useable asphalt concrete oil from the processed shingles or processed shingles/RAP mixture. Thus, the conventional method can be wasteful.
Another problem is heat loss occurs when making (or manufacturing) hot mix asphalt in the conventional method. Since the gravel is heated first, before addition of the processed shingles or processed shingle/RAP mixture, additional time and heating are necessary to activate the AC oil to be useable.
Another problem with making hot mix asphalt according to the conventional method is that rejuvenating oil, emulsification oil, liquid silicone and antistrip agents are added in the last step. This makes the conventional method inflexible in that these substances are the last step.
There is a need in the hot mix asphalt industry for an improved method of making hot mix asphalt that increases extraction of useable AC oil, minimizes heat loss in the making of HMA, and eliminates or minimizes addition of a separate asphalt concrete oil, and allows for more flexible addition of emulsification oil and antistrip agents during the manufacture of the pavement composition.